A. Field of the Invention
The present invention relates to duct work used to convey air for heating, ventilating or air conditioning structures such as commercial and industrial buildings, as well as residences. More particularly, the invention relates to air turning structures utilized at locations in the duct work where air flow direction changes.
B. Description of Background Art
Flowing air used to ventilate, heat, or cool buildings is typically routed through elongated, straight rectangular cross-section tubes or ducts, which are collectively referred to as duct work. Changes in the orientation or bearing of ducts is usually performed by means of an angled transition section or elbow, typically bent at 90 degrees and having rectangular or circular openings for attachment to separate ducts oriented at 90 degrees with respect to one another. When air flowing through a duct impacts the side wall of an elbow section disposed perpendicularly to the flow direction, substantial turbulence is created in the flowing air mass, even when the flow velocity is relatively modest. This turbulence impedes air flow, causing an increase in static pressure and pressure loss coefficients, thus necessitating the use of larger blowers that consume increased drive power, to maintain a given air flow rate at the outlet of the elbow section. Moreover, undesirable vibration and noise may be generated within the duct work, if the turbulence is sufficiently great.
For the reasons stated above, ventilation elbows or transition sections are often constructed to include means for minimizing turbulence, usually by encouraging laminar flow within the elbow. Thus, ventilation elbows constructed to minimize turbulence typically employ a plurality of curved, parallel blades or turning vanes spaced apart at regular intervals, to promote laminar air flow where the direction of air flow changes within the elbow. Typical turning vane assemblies use a plurality of curved sheet metal vanes disposed between a pair of flat, parallel metal sheets, often referred to as rails. The assembly is secured within an angled transition section or elbow.
Turning vane assemblies which employ a variety of techniques for fastening turning vanes to rails has been disclosed in the following U.S. patents:
Steffens, U.S. Pat. No. 2,292,246, Aug. 4, 1942, Duct Turn: Discloses curved double wall non-metallic duct turns or vanes having a metal insert with a tab that fits into slots cut longitudinally inward from the diagonal end wall of a duct shell, the tab having a protruding finger which is bent flush with the diagonal end wall.
Speiser, U.S. Pat. 2,826,221, Mar. 11, 1958, Duct Devices: Discloses duct devices that utilize vanes in the shape of a rectangular plate curved to form a partition wall or guide plate having parallel top and bottom horizontal edges and parallel vertical side edges. Both the top edge and bottom edge of each vane have formed therein a pair of vertically disposed cuts, forming at each cut two tongues, for a total of four tabs. This vane construction requires the provision in each plate or rail of a pair of longitudinally disposed channels or grooves having a V-shaped transverse cross-section The grooves are formed by downwardly converging walls intersecting on fold line. Each groove or channel has formed therein a plurality of longitudinally spaced apart obliquely disposed slots to receive a pair of tongues, which must be peened over in opposite directions flush with the bottom walls of the V-shaped groove to retain a vane in position between the rails.
Gracer, U.S. Pat. No. 2,861,597, Nov. 25, 1958, Air Guide Device: Discloses single and double wall turning vanes secured in slots formed in the bottoms of dimples protruding inward from rails, by deforming lateral edge walls of the vanes protruding outwards through the slots.
Perlin, U.S. Pat. No. 2,884,956, May 5, 1959, Air Guide Device: Discloses flanged, slotted cup-shaped members inserted through, holes formed in a pair of opposed side plates, to secure between the side plates turning blades positioned in the slots.
Gracer, U.S. Pat. No. 2,959,195, Nov. 8, 1960, Air Guide Device: Discloses an air turning assembly having a plurality of curved, rectangular plan view turning vanes or blades that are secured to a pair of rails by crimping opposite lateral edges of the blades protruding outwards through slots in inwardly extending protuberances formed in the rails.
Chesser, U.S. Pat. No. 3,050,160, Aug. 21, 1962, Sheet Metal Connection And Method For Effecting Same: Discloses a sheet metal connection employing a tongue protruding perpendicularly from a first plate inserted through a slot in a second plate, deformations being formed outwards from the plane of the tongue to lock it in place relative to the second plate.
Noll, U.S. Pat. No. 3,075,450, Jan. 29, 1963, Cap Assembly: Discloses a hollow tubular cap assembly having the shape of the frustrum of a cone, connectable to a cylindrical tube by extending flexible straps.
Bohannon, U.S. Pat. No. 3,144,204, Aug. 11, 1964, Centrifugal Blower Wheel: Discloses a centrifugal blower wheel having double-wall, air-foil shaped blades having a plurality of tabs protruding from opposite straight side walls thereof, the tabs on the two walls of each blade being inserted into first and second groups of slots provided through front and rear circular end plates, and bent over to retain the blades in place.
Olmsted, et al., U.S. Pat. No. 3,224,668, Dec. 21, 1965, Blower Wheel Wedged End Blade Mounting: Discloses curved blower wheel blades attachable to annular side rings by a central finger or tongue protruding from opposite short lateral edges of the blade. The fingers are bent into a V-shape, inserted into semi-circular or triangular-shaped holes through the side rings, and bent over to retain the blades in the rings.
Jacobsen, U.S. Pat. No. 3,381,713, May 7, 1968, Turning Vane And Rail Construction: Discloses double-wall, airfoil-shaped turning vanes having formed in the inner side of one wall a pair of cylindrically-shaped passageways disposed perpendicularly inwards from the outer lateral edge of the wall. Headed pins or nails are driven through holes provided in a pair of parallel side rails into the passageways, to secure the vanes to the rails.
Harper, U.S. Pat. No. 3,405,737, Oct. 15, 1968, Duct Device: Discloses double wall vanes secured in slots cut in inwardly protruding depressions in opposed side rails.
Hinden, U.S. Pat. No. 3,494,379, Feb. 10, 1970, Air Turning Assembly And Mounting Rail: Discloses an air turning assembly which employs turning vanes formed of glass fiber impregnated with a polymer and inserted through curved apertures or sockets punched in U-cross section rails. The sockets are outlined by outwardly deflected, spaced tabs or shoulder portions which are compressed by a cam lock against the protruding portion of a vane, thereby securing the vane to the rail.
Hinden, U.S. Pat. No. 3,602,262, Aug. 31, 1971, Air Turning Assembly: Discloses an air turning assembly utilizing fibrous, compressible vane members secured to a pair of parallel rails between the sides of a U-shaped clamp protruding inward from a rail and secured thereto.
Myers, U.S. Pat. No. 4,467,829, Aug. 28, 1984, Turning Vane Rail: Discloses a rail for mounting sheet metal turning vanes that includes a sheet and integral vane guides extending generally perpendicularly away from the plane of the sheet. Each vane guide is a plate slit from the sheet except for one edge along which the plate is bent. The plate is adapted to be positioned adjacent to a wall of the vane. An access aperture, partially located in the sheet and partially located in the plate is adapted to allow access to a portion of the vane wall for contact by a striking tool. A blow from the tool splits the sheet metal vane wall to form tabs which are folded through the aperture, which securely attaches the wall to the rail.
DeLord U.S. Pat. No. 4,641,684, Feb. 10, 1987, Rail For An Air Turning Vane Assembly: Discloses an air turning vane assembly in which the vanes are attached to tabs formed in each rail by integral locking clips formed upon the rail tabs. The rail assembly is constructed from rails having cutout portions adapted to receive the tabs of similar rails, to permit compact nesting for storage and shipping. The assembly requires use of a special locking tool that has a cutting tooth which cuts a ribbon in a vane wall to form an integral locking clip for securing the vanes to rails.
Myers, U.S. Pat. No. 4,911,205, Mar. 27, 1990, Apparatus And Method For Duct Vane Mounting: Discloses a duct vane assembly having rails in which a pair of inwardly projecting, rectangular tabs lying in an arc are formed. Each tab is insertably secured in a laterally disposed slot formed near the outer lateral edge of each curved turning vane, the slot being defined by a lateral strap formed in the vane adjacent its end. A finger bent in the end of a rail tab projects into an opening in the vane adjacent the strap to positively retain the vane connected to the rails.
Felson, U.S. Pat. No. 5,068,957, Dec. 3, 1991, Turning Vane Setting Tool: Discloses a device and method for permanently anchoring air turning vanes to manufactured vane rails or runners in duct work systems that utilizes pre-positioning, splitting and bending means combined into one continuous sequence when the tool is applied to the exposed edge of an air turning vane which has been inserted into the slotted depression of manufactured vane rails or runners and is activated by means of a hammer blow or similar energy source.
Lyons, et al., U.S. Pat. No. 5,181,314, Jan. 26, 1993, Apparatus For Manufacturing Air Turning Assembly: Discloses an apparatus and method for forming air turning assemblies. The vanes are conventional bowed rectangular sheets, the lateral edges of which are secured in slotted projections on the inner surface of each rail by chisel lips entering the slots in projections and bending over the edges of the vane protruding therethrough.
The Gracer, Felson and Lyons, et al. patents all disclose a turning vane and rail construction which requires the formation of slotted depressions in the rails to secure the vanes thereto. The Hinden '379 patent discloses a turning vane assembly which uses tabs projecting outward from the perimeter of an aperture through a flat rail which are compressed by a locking cam against the perimeter of a compressible vane protruding through the aperture. The Hinden '262 patent discloses the use of a U-shaped compression bracket protruding inwards from a rail and attached thereto by a pop rivet to compress the end of a resilient vane, to which it is secured by another pop rivet. DeLord discloses a rail for a turning vane assembly that utilizes tabs bent inwards from apertures in the rail to attach to an integral locking clip formed in the end wall of a vane by a special tool. Myers discloses a vane and rail construction which utilizes a strap formed near each end of a vane by a laterally disposed slot, the slot insertably receiving a tab bent out from an aperture formed in a rail and secured to the vane by a finger bent out from the end of the tab.
Vane and rail assemblies known to the present inventor, including those cited above, generally require that portions of sheet metal vanes or rails be deformed by robustly pounding parts thereof, using either a hammer, chisel, or specially designed tools, to fasten the vanes and rails together. Sometimes, pounding on a vane and rail assembly to install a series of vanes can loosen the fastening of vanes installed earlier. Then, when a completed vane and rail assembly has been installed into a duct work elbow; and the latter installed in a building, variations in the pressure of air flowing through the duct work can cause the "cheeks" or walls of curved transition sections to expand and contract, and perpendicular duct walls to flex inward and outward or "oil-can" in response to air pressure fluctuations. Since environment control systems for buildings require that air flow rate be turned on and off intermittently, or varied by control dampers, duct work air turning vane assemblies are routinely subjected to such wall deformations. As a result, vanes which had been initially loosened during the fabrication of a turning vane and rail assembly can become completely detached from the rails long after duct work has been installed in a building. As can be readily appreciated, replacing dislodged turning vanes can be an extremely time consuming, laborious and expensive process, particularly in high-rise buildings.
The present invention was conceived of to provide an improved air turning vane and rail assembly of simplified construction and greater versatility than existing assemblies, in which vanes self-lock into engagement with rails, thereby minimizing the likelihood of vanes dislodging from a vane and rail assembly.